The present invention relates to an rpm regulator for fuel injection pumps associated with internal combustion engines of the type having a pivotable control lever which actuates a fuel quantity control sleeve of the injection pump. The control lever is urged to pivot by an rpm-dependent force which is opposed by the force exerted by a regulating spring assembly located in the suction chamber of the injection pump. The regulating spring assembly can be arbitrarily pre-compressed by an adjustment lever, and it includes at least one control spring lodged in a holding device consisting of two holding members.
When it is desired to obtain a low degree of variation during terminal downward regulation in fuel injection pumps which use centrifugal governors as rpm signal generators, the regulator springs must be weak (soft), and they may also be pre-compressed. Alternatively, a combination consisting of several springs of which one is a weak, pre-compressed spring, may be provided. The limit of the achievable degree of variation is set by the degree of softness of the spring which is used as a control spring in the injection pump while avoiding negative influences on the control process caused by the high frequency mechanical oscillations generated in the operation of the injection pump. Such influences would adversely affect the fuel regulation and hence also the quiet and smooth running of the internal combustion engine which is supplied by the injection pump.
A known regulator of the above-described type uses a tension spring which has one end hooked onto a first connecting member between a setting lever and a control lever and has the other end hooked onto a second connecting member between the setting lever and the control lever. The second connecting member is pressed by the tension spring against the head of a screw threaded into the first connecting member, with the pre-compression of the tension spring being determined by the depth of insertion of the screw.
This arrangement has the disadvantage that the hook-on points of the spring can be unintentionally displaced, which would result in a change of the pre-compression of the spring during the operation of the pump. In addition, this mechanism is not stable with respect to lateral forces and buckling. Furthermore, when the regulator regulates downwardly, i.e. toward shut-off, and the second connecting member lifts off from the head of the screw, and oscillation of the entire assembly may occur. In this installation the setting lever at first determines the injected fuel quantity by means of the pre-compressed spring. The soft spring becomes effective only in the case of downward regulation and only after the pre-compression of the control spring has been overcome by the centrifugal force governor, so that, as has already been described above, a certain degree of variation determined by the softness of the spring, may be achieved. However, this degree of variation cannot be as small as desired due to the propensity of this arrangement to malfunction.
Another rpm governor is known in which centrifugal forces displace a bushing on a shaft against the force of a control spring. This bushing is provided with a throttle aperture for the purpose of damping any oscillations; during changes of the volume enclosed between the shaft and the bushing, fuel is displaced through the throttle aperture. In this way, mechanical oscillations which might affect the regulator are damped throughout the entire effective domain of the rpm governor. However, this mechanism cannot achieve precise damping aimed at special operational points and at the conditions prevailing there. In particular, it might be undesirable if the damping effect in the middle operational domain were too high to permit a sufficiently fast-acting control process.